[jh_f30]

The difference in unsprung weight with a smaller rotor probably isn't worth the increased likelihood of fade that will come from cooking your brakes on a circuit. The whole point of bigger brakes isn't to increase stopping power, it's to resist brake fade from overheating. Greater mass takes longer to heat up and larger surface area lets them cool faster.

Tenths or hundredths of a second saved from lighter rotors is completely moot if your brakes overheat and you can't finish the race. The biggest advantage of carbon ceramics is heat dissipation, not necessarily weight savings.

[skier_du]

Originally Posted by jh_f30

The difference in unsprung weight with a smaller rotor probably isn't worth the increased likelihood of fade that will come from cooking your brakes on a circuit. The whole point of bigger brakes isn't to increase stopping power, it's to resist brake fade from overheating. Greater mass takes longer to heat up and larger surface area lets them cool faster.

Tenths or hundredths of a second saved from lighter rotors is completely moot if your brakes overheat and you can't finish the race. The biggest advantage of carbon ceramics is heat dissipation, not necessarily weight savings.

Originally Posted by johnung

Great point! Tires are the other part of braking and certainly some tires are much better in the rain than others. Both in handling and braking.

I have summer Michelin Pilot Sport 4S tires that are very high rated in dry and wet. Even in the pouring rain I have a difficult time telling the difference. MPS4S would be perfect for a warm rainy climate.

If you are getting new tires don't miss out on the chance to upgrade tire size on your same wheels. I upgraded from stock size 225/45-18 to 245/40-18 which provides the best handling on my BMW Model 400M stock 18" wheels. I could have also chosen 245/45-18 which would have provided great handling and more comfort, along with filling wheel wells more for a dropped look.

I'm in NJ so in winter when it hits 40 degrees Fahrenheit in December I change to winter Michelin X-ICE Xi3 in 225/45-18. (I went back to stock size width based on recommendations that the 225 width would cut through snow itself better than 245 width which could tend to sort of hydroplane over the snow surface instead of digging in) This is my first winter on actual specialized winter tires. I love the way the rubber gets more supple as the temperature drops. They are also superior in rain and on ice. Got caught in a recent flash ice/snow storm and I just drove around on it while other cars were spinning wheels and being pushed by hand off the road.

Someone please correct me if I'm wrong but since the F36 Gran Coupe is based on the F32-33 then the brakes should be the same.

TWO PIECE ROTORS- When are they an advance?

Sometimes you hear people mention advantages of two-piece brake rotors. But the actual details of why that may be and if the advantage is worth much gets lost as guys just repeat the statement with no history and no explanation.

There is a huge advantage to two-piece rotors but only if they are talking about very expensive true full-floating two-piece rotors. You see them on the racetrack such as BremboGT brakes.

They reduce unsprung weight with a lightweight rotor ring that's replaceable. The heat exchange and pad alignment under harsh heat conditions (racing) is superior with a full floating design. StopTech is the only one that I know of that makes them in a BMW stock size of 370mm x 30mm and they are usually a 6-8 week wait to custom make them. I have them on my car.

Note: I'm not trying to talk anyone out of buying two-piece riveted rotors. They look cool. I would buy them. But there isn't some huge noticeable advantage to them.

Usually when guys talk about two-piece rotors they mean the rotors that you see with big rivets all around. Instead of being a one-piece steel rotor, they have a slightly lower weight aluminum rotor hat rigidly attached with the rivets to a solid steel rotor ring. They look cooler with the rivets but there is little true unsprung weight savings.

To illustrate my point, if you had front Brembo 4-piston calipers over 340mm x 30mm rotors, the plain one-piece rotors weigh 24.0 lbs each. The same size rotor in a riveted two-piece weighs 22.0 lbs.

So the typical response is that's great and worth it to me to pay more for a two-piece rotor and save 2lbs of unsprung weight. But 2lbs isn't much so don't expect to actually feel a difference.

So say that you want to make the investment and upgrade your front brakes to the Brembo 4-piston calipers that ride over 370mm x 30mm rotors. That sounds like a huge upgrade.

Well, the 370mm x 30mm plain one-piece rotors weigh 29.1 lbs each! And even the two-piece plain riveted rotors weigh 26.5 lbs each. Also the aluminum castings for the 370 calipers are larger so they weigh more than the 340 calipers.

So it's always a trade-off, you can try to save a little unsprung weight here and there with riveted rotors but ultimately unsprung weight is added whenever you go to bigger brakes.

FYI- Zimmermann makes a two-piece riveted plain 370x30 front rotor part number 150.2911.32 and a rear two-piece riveted plain 345mm x 24mm part number 150.2919.32 (for a 185mm emergency brake which is the most common size)

RACING-
The thought just occurred to me is that for racing an F3x with stock brakes, the best front brakes are probably the Brembo 4-piston over 340mm x 30mm rotors. They have the same pad and piston size as the 370 brakes, but with much lower overall unsprung weight.

The lightest rotor I've found in that 340 size is the ECS semi-floating drilled & slotted rotor which is 20.95 lbs compared to Zimmermann plain two-piece riveted at 22.0 lbs. ECS claims a huge weight savings of 3.5 lbs which I guess is versus the heaviest rotor they could possibly find. It's really only a 1.05 lb weight savings over a two-piece plain rotor, and some of that is from the material loss of cross-drilling and machining the slots.

So if I was racing with F3x stock brakes, my ideal setup would include:
Brembo 340mm front calipers
ECS 340mm Semi-Floating rotors
Racing Brake Pads
Stainless steel brake lines
Racing brake fluid

For rear racing brakes:
The 1-piston Bosch calipers over 330mm x 20mm would definitely have the lowest unsprung weight but they just don't match well with the weight of the car and cause the car to nose dive under extreme braking. So I'd expect the better racing choice to be the 2-piston Brembo calipers over 345mm x 24mm rotors. Even though the rear unsprung weight would be greater so would the brake performance.

Link to ECS Rotors
https://www.ecstuning.com/b-ecs-part...0/014586ecskt/

I won't say much for rotors on the street as I believe the different options make little to no difference for the vast majority of people on the street. So just get what you like for your budget.
But on the track, small things make big differences. I've been tracking mine with the 340 brakes, and it's hard because it's not a big enough heat sink. Yes, lower unsprung mass does help the suspension and handling and should be done whenever possible, but the 340 isn't really sufficient for the weight of an f30 with really sticky track tires. I have custom brake scopes, Hawk DTC30 pads and factory style Brembo rotors with RBF 660 fluid and it's barely enough. If I had slicks it would overwhelm them with heat. I've just been running the 200tw tires for the time being. The F80 seems to be good with the 380 on street tires and even some on R comps depending on driving style and the track. But they're still struggling with slicks.
Also I wouldn't run the drilled on track. My friends and I have seen those rotors crack. Heck, I had Stop Tech Cryo-Treated and slotted Sport Rotors crack after just a handful of track days. The riveted, plain Brembo rotors are holding up better.

[Onizukachan]

Originally Posted by FalcoFury

You have no idea how much this helps! You're so right about rotars. It seems some people care more about how they look. Last thing I want is more noise. Although I probably hear it after I get my parts installed and tune.

The one thing I want out of rotors is the rain performance. If you know anything about Florida, we get a lot of rain. So I'll definitely consider upgrading to the cross-drilled you recommend.

To confirm, yes I have OEM m-sport brake package blue calipers and everything from factory.

Thank you for all the part numbers as well. You saved me so much time on research, etc. I'll start with brake lines and pads!

You don’t need drilled rotors for rain, if you did, all cars would hav3 them stock. I’m from the south and the drilling is for pad outgassing at the track. Solids are perfectly fine up to Cat 4 Hurricanes and water a foot deep and are the best for street use... unless you have a habit of doing 0-150-0 runs between every stop sign and trying to overheat your street pads?

Anyone who thinks they see better performance in the rain from holes should stop driving in the creek and get back on the street. And yes, the holes make noise, they wear the pads down faster, they reduce the performance and heat sink of the rotor and are primarily cosmetic as far as street use is concerned.

[johnung]

Originally Posted by Onizukachan

You don’t need drilled rotors for rain, if you did, all cars would hav3 them stock. I’m from the south and the drilling is for pad outgassing at the track. Solids are perfectly fine up to Cat 4 Hurricanes and water a foot deep and are the best for street use... unless you have a habit of doing 0-150-0 runs between every stop sign and trying to overheat your street pads?

Anyone who thinks they see better performance in the rain from holes should stop driving in the creek and get back on the street. And yes, the holes make noise, they wear the pads down faster, they reduce the performance and heat sink of the rotor and are primarily cosmetic as far as street use is concerned.

I respectfully disagree, and here's why. My experience has been the opposite. Many top manufacturers put drilled rotors on their stock models including Mercedes, McLaren, Porsche and more.

Outgassing was one reason to use drilled rotors way back in the 1980's because pad materials used then produced gases under heat and friction. The cross-drilled holes gave the gases a place to go to remove the negative effect on braking. Brake pad materials have been completely different now for a long time so outgassing is an outdated issue.

I know for a fact that cross-drilled rotors have the best bite on the street in the rain because I've tested three different brake configurations on my F3x. When planning my current configuration, which has cross-drilled rotors front and back, I actually consulted with an expert who sells brakes to race teams for a living. He took me through the engineering to identify the best combination of street performance brake components for my car. Later the owner of a mod house drove my car and remarked that my brakes were better than his. And he's done several brake mods and tracks his car.

[johnung]

Originally Posted by skier_du

I won't say much for rotors on the street as I believe the different options make little to no difference for the vast majority of people on the street. So just get what you like for your budget.
But on the track, small things make big differences. I've been tracking mine with the 340 brakes, and it's hard because it's not a big enough heat sink. Yes, lower unsprung mass does help the suspension and handling and should be done whenever possible, but the 340 isn't really sufficient for the weight of an f30 with really sticky track tires. I have custom brake scopes, Hawk DTC30 pads and factory style Brembo rotors with RBF 660 fluid and it's barely enough. If I had slicks it would overwhelm them with heat. I've just been running the 200tw tires for the time being. The F80 seems to be good with the 380 on street tires and even some on R comps depending on driving style and the track. But they're still struggling with slicks.
Also I wouldn't run the drilled on track. My friends and I have seen those rotors crack. Heck, I had Stop Tech Cryo-Treated and slotted Sport Rotors crack after just a handful of track days. The riveted, plain Brembo rotors are holding up better.

Great information from your tracking. Thanks for sharing. It's so hard to know what factor is more important without that valuable experience. Definitely wouldn't run drilled rotors on lap after lap tracking. They aren't designed to hold up to those extreme heat levels.

[FalcoFury]

Originally Posted by johnung

Great information from your tracking. Thanks for sharing. It's so hard to know what factor is more important without that valuable experience. Definitely wouldn't run drilled rotors on lap after lap tracking. They aren't designed to hold up to those extreme heat levels.

This kind of information is invaluable from people with first hand experience. I'm quite a long ways away from taking my car to a track but I'm on a good pace. After I get my engine mods/bolt ons installed and tuned, I'm going to get the new brakes. Sometime next month I'll get the brakes, then along with tires. When that's all installed, I feel like I'll be ready to hit the track.

Thanks so much to everyone in this topic.

[johnung]

Originally Posted by FalcoFury

This kind of information is invaluable from people with first hand experience. I'm quite a long ways away from taking my car to a track but I'm on a good pace. After I get my engine mods/bolt ons installed and tuned, I'm going to get the new brakes. Sometime next month I'll get the brakes, then along with tires. When that's all installed, I feel like I'll be ready to hit the track.

Thanks so much to everyone in this topic.

My car mods are all for street performance. I'm sure my car would hold its own for a few laps but track cars need different components depending on type of tracking. Often plain or slotted rotors, ceramic racing pads, race brake fluid every six months, different tires for racing, larger intercoolers. Safety equipment like helmets, fire systems, roll cages, etc.

I'd suggest hanging out at the track and talking with guys on the forums who do the type of racing that interests you.

[FalcoFury]

I'm not sure what tracks I should go to that are near me, and I can't figure out where to look or what to search for. I'm in Northeast Florida.

[johnung]

Originally Posted by FalcoFury

I'm not sure what tracks I should go to that are near me, and I can't figure out where to look or what to search for. I'm in Northeast Florida.

Suggest going to the regional forum for your Florida area here on Bimmerpost and asking. Also search for FaceBook BMW groups in your area and you are bound to find track guys there.

[Gen13 F36]

Originally Posted by FalcoFury

I'm not sure what tracks I should go to that are near me, and I can't figure out where to look or what to search for. I'm in Northeast Florida.

You should check out BMW CCA if they have an active Florida chapter.